## NULL값 제외시키 전
![널값 포함](https://s3.us-west-2.amazonaws.com/secure.notion-static.com/61f0a95e-21f5-41b5-865c-14c387264e2c/Untitled.png?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=AKIAT73L2G45O3KS52Y5%2F20211013%2Fus-west-2%2Fs3%2Faws4_request&X-Amz-Date=20211013T164305Z&X-Amz-Expires=86400&X-Amz-Signature=d175ced29c3480bf2404a4d9b807e975909e520087802f3829bc4f33e0c70d92&X-Amz-SignedHeaders=host&response-content-disposition=filename%20%3D%22Untitled.png%22)

## 제외 후 `test_sort_values`
![제외 후](https://s3.us-west-2.amazonaws.com/secure.notion-static.com/49473de7-cf62-425a-8cbf-a6ad6841701a/Untitled.png?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=AKIAT73L2G45O3KS52Y5%2F20211013%2Fus-west-2%2Fs3%2Faws4_request&X-Amz-Date=20211013T164332Z&X-Amz-Expires=86400&X-Amz-Signature=c8dec63e212e1c49cfafcb21b4b00a0c876a91ef38f4a3d9446f906cab9473d2&X-Amz-SignedHeaders=host&response-content-disposition=filename%20%3D%22Untitled.png%22)
2346만가지나 된다. NULL값은 다 누락시켰는데, 전보다 가지수가 증가함. 아마도 널값은 누락시키고 각각의 값들이 생겨나서 가짓수가 훨씬 증가 한 것 같다.